问题 多选题

矩形线圈abcd位于足够长的通电直导线附近,且线圈平面与导线在同一平面内,如图所示,线圈的两条边ad和bc与导线平行,要使线圈中产生abcda方向的电流,可以(  )

A.线圈不动,增大导线中的电流

B.线圈不动,减小导线中的电流

C.导线中的电流不变,线圈向右平动

D.导线中的电流不变,线圈向上平动

答案

A、当电流增大时,垂直纸面向里的磁场,穿过线圈的磁通量增加,根据楞次定律可知,感应电流方向逆时针.故A错误.

B、当电流减小时,垂直纸面向里的磁场,穿过线圈的磁通量减小,根据楞次定律可知,感应电流方向顺时针.故B正确.

C、当在线圈平面内,垂直bc边向右拉动线圈,逐渐远离线圈,穿过线圈的磁场减小,即穿过线圈的磁通量减小,故产生感应电流为顺时针,即感应电流的方向为abcda.故C正确.

D、导线中的电流不变,线圈向上平动,穿过线圈的磁场不变,即穿过线圈的磁通量也不变,则不产生感应电流,故D错误.

故选BC.

单项选择题 A3/A4型题
完形填空

II. 完形填空

Coming home from school that dark winter day so long ago, I was filled with excitement of having the weekend off. But I was   31   into stillness by what I saw. Mother, seated at the far end of the sofa, was    32   , with the second--hand green typewriter on the table. She told me that she couldn't    33    fast and then she was out of work. My shock and embarrassment at finding Mother in tears was a perfect proof of how    34    I understood the pressure on her. Sitting beside her on the sofa, I began very slowly to understand. "I guess we all have to   35   something," Mother said quietly. I could   36    her pain and the tension of   37   the strong feeling that were interrupted by my   38    . Suddenly, something inside me lit up. I reached out and put my arms around her. She broke then. She put her face    39   my shoulder and sobbed. I held her   40   and didn't try to talk. I knew I was doing what I should, what I could and that was   41   . At that moment, feeling Mother's   42    with feelings, I understood for the first time her being easy to   43   . She was still my mother,   44   she was something   45    : a person like me, capable of fear,   46   and failure. I could feel her pain as she must have felt mine on a thousand occasions when I sought   47   in her arms.

A week later Mother took a job selling dry goods at half the salary the radio station   48   .

"It's a job I can do, though." She said simply. But the evening practice on the green typewriter continued. I had a very   49   feeling now when I passed her door at night and heard her  50   away across the paper. I knew there was something more going on in there than a woman learning to type.

31. A. fooled  B. tricked       C. puzzled      D. shocked

32. A. crying  B. smiling      C. thinking     D. whispering

33. A. write    B. type    C. run     D. wash

34. A. eagerly B. worriedly   C. hurriedly    D. happily

35. A. fail      B. win     C. forget D. gain

36. A. realize  B. understand  C. sense   D. recognize

37. A. holding back       B. putting away      C. holding on  D. stopping from

38. A. pain     B. laughter     C. arrival D. cry

39. A. by     B. upon   C. beside D. against

40. A. tightly  B. rudely C. carefully    D. politely

41. A. enough B. little   C. all      D. nothing

42. A. hand     B. face    C. hair    D. back

43. A. content B. break  C. fall     D. shout

44. A. therefore      B. although     C. yet      D. however

45. A. more    B. excellent    C. strange       D. huge

46. A. wound  B. pride   C. success       D. hurt

47. A. kindness      B. memory     C. comfort      D. support

48. A. supplied       B. offered       C. paid    D. contributed

49. A. different      B. hard    C. pleasant      D. serious

50. A. crying  B. laughing     C. tapping      D. sewing